349 research outputs found
Determining An Individualâs 3-Dimensional Body Shape From Two 2-Dimensional Photographic Images
Poikos are interested in the process of determining an individualâs 3-D body shape from two 2-D images taken with standard hardware such as a camera phone or web cam. The study group addressed two particu- lar issues in the overall process that Poikos would like to improve on, a markerless correction for radial distortion and improved segmentation of the personâs outline from the image. Based on a radial distortion func- tion the study group deduced and implemented an optimization method for finding the function parameters given straight lines in the distorted image. For the segmentation problem, the study group applied Perona- Malik pre-processing to improve edge detection in the image. An open source version of the âsegmentation by weighted aggregationâ method was applied to the images and shows considerable promise. Together with prior information of the content of the image, this algorithm could provide better results than the current Poikos segmentation method
Electromagnetic Decays of Heavy Baryons
The electromagnetic decays of the ground state baryon multiplets with one
heavy quark are calculated using Heavy Hadron Chiral Perturbation Theory. The
M1 and E2 amplitudes for S^{*}--> S gamma, S^{*} --> T gamma and S --> T gamma
are separately computed. All M1 transitions are calculated up to
O(1/Lambda_chi^2). The E2 amplitudes contribute at the same order for S^{*}-->
S gamma, while for S^{*} --> T gamma they first appear at O(1/(m_Q
\Lambda_\chi^2)) and for S --> T gamma are completely negligible. The
renormalization of the chiral loops is discussed and relations among different
decay amplitudes are derived. We find that chiral loops involving
electromagnetic interactions of the light pseudoscalar mesons provide a sizable
enhancement of these decay widths. Furthermore, we obtain an absolute
prediction for the widths of Xi^{0'(*)}_c--> Xi^{0}_c gamma and Xi^{-'(*)}_b-->
Xi^{-}_b gamma. Our results are compared to other estimates existing in the
literature.Comment: 17 pages, 3 figures, submitted to Phys. Rev.
Nonexotic Neutral Gauge Bosons
We study theoretical and experimental constraints on electroweak theories
including a new color-singlet and electrically-neutral gauge boson. We first
note that the electric charges of the observed fermions imply that any such Z'
boson may be described by a gauge theory in which the Abelian gauge groups are
the usual hypercharge along with another U(1) component in a kinetic-diagonal
basis. Assuming that the observed quarks and leptons have
generation-independent U(1) charges, and that no new fermions couple to the
standard model gauge bosons, we find that their U(1) charges form a
two-parameter family consistent with anomaly cancellation and viable fermion
masses, provided there are at least three right-handed neutrinos. We then
derive bounds on the Z' mass and couplings imposed by direct production and
Z-pole measurements. For generic charge assignments and a gauge coupling of
electromagnetic strength, the strongest lower bound on the Z' mass comes from
Z-pole measurements, and is of order 1 TeV. If the new U(1) charges are
proportional to B-L, however, there is no tree-level mixing between the Z and
Z', and the best bounds come from the absence of direct production at LEPII and
the Tevatron. If the U(1) gauge coupling is one or two orders of magnitude
below the electromagnetic one, these bounds are satisfied for most values of
the Z' mass.Comment: 26 pages, 2 figures. A comparison with the LEP bounds on sneutrino
resonances is include
A CsI(Tl) Scintillating Crystal Detector for the Studies of Low Energy Neutrino Interactions
Scintillating crystal detector may offer some potential advantages in the
low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed
near the core of Nuclear Power Station II in Taiwan is being constructed for
the studies of electron-neutrino scatterings and other keV-MeV range neutrino
interactions. The motivations of this detector approach, the physics to be
addressed, the basic experimental design, and the characteristic performance of
prototype modules are described. The expected background channels and their
experimental handles are discussed.Comment: 34 pages, 11 figures, submitted to Nucl. Instrum. Method
Chiral effective field theories of the strong interactions
Effective field theories of the strong interactions based on the approximate
chiral symmetry of QCD provide a model-independent approach to low-energy
hadron physics. We give a brief introduction to mesonic and baryonic chiral
perturbation theory and discuss a number of applications. We also consider the
effective field theory including vector and axial-vector mesons.Comment: 22 pages, 9 figures, proceedings of "Many-Body Structure of Strongly
Interacting Systems", Mainz, Germany, Feb. 23-25 201
Categorizing Different Approaches to the Cosmological Constant Problem
We have found that proposals addressing the old cosmological constant problem
come in various categories. The aim of this paper is to identify as many
different, credible mechanisms as possible and to provide them with a code for
future reference. We find that they all can be classified into five different
schemes of which we indicate the advantages and drawbacks.
Besides, we add a new approach based on a symmetry principle mapping real to
imaginary spacetime.Comment: updated version, accepted for publicatio
Measurement of the p-pbar -> Wgamma + X cross section at sqrt(s) = 1.96 TeV and WWgamma anomalous coupling limits
The WWgamma triple gauge boson coupling parameters are studied using p-pbar
-> l nu gamma + X (l = e,mu) events at sqrt(s) = 1.96 TeV. The data were
collected with the DO detector from an integrated luminosity of 162 pb^{-1}
delivered by the Fermilab Tevatron Collider. The cross section times branching
fraction for p-pbar -> W(gamma) + X -> l nu gamma + X with E_T^{gamma} > 8 GeV
and Delta R_{l gamma} > 0.7 is 14.8 +/- 1.6 (stat) +/- 1.0 (syst) +/- 1.0 (lum)
pb. The one-dimensional 95% confidence level limits on anomalous couplings are
-0.88 < Delta kappa_{gamma} < 0.96 and -0.20 < lambda_{gamma} < 0.20.Comment: Submitted to Phys. Rev. D Rapid Communication
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt{s} = 1.96 TeV using Kinematic Characteristics of Lepton + Jets Events
We present a measurement of the top quark pair ttbar production cross section
in ppbar collisions at a center-of-mass energy of 1.96 TeV using 230 pb**{-1}
of data collected by the DO detector at the Fermilab Tevatron Collider. We
select events with one charged lepton (electron or muon), large missing
transverse energy, and at least four jets, and extract the ttbar content of the
sample based on the kinematic characteristics of the events. For a top quark
mass of 175 GeV, we measure sigma(ttbar) = 6.7 {+1.4-1.3} (stat) {+1.6- 1.1}
(syst) +/-0.4 (lumi) pb, in good agreement with the standard model prediction.Comment: submitted to Phys.Rev.Let
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV using Lepton + Jets Events with Lifetime b-tagging
We present a measurement of the top quark pair () production cross
section () in collisions at TeV
using 230 pb of data collected by the D0 experiment at the Fermilab
Tevatron Collider. We select events with one charged lepton (electron or muon),
missing transverse energy, and jets in the final state. We employ
lifetime-based b-jet identification techniques to further enhance the
purity of the selected sample. For a top quark mass of 175 GeV, we
measure pb, in
agreement with the standard model expectation.Comment: 7 pages, 2 figures, 3 tables Submitted to Phys.Rev.Let
Measurement of the ratios of the Z/G* + >= n jet production cross sections to the total inclusive Z/G* cross section in ppbar collisions at sqrt(s) = 1.96 TeV
We present a study of events with Z bosons and jets produced at the Fermilab
Tevatron Collider in ppbar collisions at a center of mass energy of 1.96 TeV.
The data sample consists of nearly 14,000 Z/G* -> e+e- candidates corresponding
to the integrated luminosity of 0.4 fb-1 collected using the D0 detector.
Ratios of the Z/G* + >= n jet cross sections to the total inclusive Z/G* cross
section have been measured for n = 1 to 4 jet events. Our measurements are
found to be in good agreement with a next-to-leading order QCD calculation and
with a tree-level QCD prediction with parton shower simulation and
hadronization.Comment: 7 pages, 2 figures, slightly modified, submitted to Phys. Lett.
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